A custom behaviour for Xamarin's CollectionView control that modulates its height based on how many items it's showing. Taken from https://forums.xamarin.com/discussion/158425/collectionview-included-additional-space-at-the-bottom. Addresses: https://github.com/xamarin/Xamarin.Forms/issues/6497

CollectionViewHeightBehavior.cs

public class CollectionViewHeightBehavior : Behavior<CollectionView>
{
    bool hasHeightChanged = false;
    public CollectionView CollectionViewObject
    {
        get;
        private set;
    }
    protected override void OnAttachedTo(CollectionView bindable)
    {
        base.OnAttachedTo(bindable);
        CollectionViewObject = bindable;
        bindable.BindingContextChanged += Bindable_BindingContextChanged;
        bindable.SizeChanged += Bindable_SizeChanged;
    }


    private void Bindable_SizeChanged(object sender, EventArgs e)
    {
        var collectionHeight = CollectionViewObject.Height;

        if (CollectionViewObject.Height > 0 && !hasHeightChanged)
        {
            CollectionViewObject.HeightRequest = (collectionHeight / 2) + 20;

            hasHeightChanged = true;
        }
    }

    private void Bindable_BindingContextChanged(object sender, EventArgs e)
    {
        OnBindingContextChanged();
    }

    protected override void OnBindingContextChanged()
    {
        base.OnBindingContextChanged();
        BindingContext = CollectionViewObject.BindingContext;
    }
    protected override void OnDetachingFrom(CollectionView bindable)
    {
        base.OnDetachingFrom(bindable);
        bindable.BindingContextChanged -= Bindable_BindingContextChanged;
        bindable.SizeChanged -= Bindable_SizeChanged;
    }
}

/* To consume in XAML:
<CollectionView.Behaviors>
    <behavior:CollectionViewHightBehavior/>
</CollectionView.Behaviors>
*/